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If 6,18,39, and x are in proportion, then find the value of x.
117
112
139
115
117
In a proportion a:b::c:d, the product of extremes equals the product of means. Thus, 6 * x = 18 * 39. Dividing both sides by 6 gives x = 3 * 39 = 117.
Four numbers 6, 18, 39, and x are in proportion.
a:b::c:dтЯ╣baтАЛ=dcтАЛтЯ╣a├Чd=b├Чc
In a proportion a:b::c:d, the product of extremes equals the product of means. Thus, 6 * x = 18 * 39. Dividing both sides by 6 gives x = 3 * 39 = 117.
Many students set up the ratio as 6/18 = x/39 instead of 6/18 = 39/x, or fail to simplify the fraction before multiplying.
Setup the proportion
If four numbers a, b, c, d are in proportion, they satisfy the relation a/b = c/d.
186тАЛ=x39тАЛ
Cross-multiply
Multiply the extremes (6 and x) and the means (18 and 39) to solve for x.
6├Чx=18├Ч39
Calculate x
Divide 18 by 6 to simplify the calculation, then multiply the result by 39.
x=618тАЛ├Ч39=3├Ч39=117
A is correct because the proportional relationship leads to x = (18 ├Ч 39) / 6, which equals 117.
This concept is fundamental to solving problems in Speed-Distance-Time (as speed is proportional to distance) and Work-Time variations.
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